LAUSR

Ceramic electrolytes (CEs) and solid polymer electrolytes (SPEs) are considered to be effective methods to suppress the growth of lithium dendrites. But the inferior wettability of CEs and the low ionic conductivity of SPEs limit their applications. Zhang and colleagues report in Advanced Materials that flexible ceramic/polymer hybrid solid electrolyte—prepared by in situ coupling reaction—has great promise for high-performance Li metal batteries (LMBs). Ultrahigh energy density of LMBs is catching worldwide attention, which are 2 to 6 times higher than that of lithium-ion batteries (LIBs) [1]. However, the potential safety of LMBs brought by uneven dendrites restricts the application [2]. CEs and SPEs are regarded as the most effective way to resolve the dendrites issues [3]. Li7La3Zr2O12 (LLZO) and Li10GeP2S12 (LGPS) and other typical CEs show high shear modulus, and the lithium-ion transference number tLiþ ð Þ is closing to 1, nevertheless the dendrites may grow through crystal boundary even under the low current density because of the maldistribution of electric field [4, 5]. What is more, the inferior wettability of CEs may cause increased interface resistance and decreased energy transform efficiency. In addition, Li ions migrate though polymer segments for SPEs, so the ionic conductivity and electrochemical performance are restricted by the polymer structure. Recently in Advanced Materials, Zhang and colleagues reported a flexible ceramic/polymer hybrid solid electrolyte (HSE) for solid LMBs [6]. The schematic illustration of HSE is shown in Fig. 1a. LGPS and polyethylene glycol (PEG) are binding by chemical bonds under the help of (3chloropropyl)trimethoxysilane (CTMS) which is acting as bridge builder. The authors believe the reaction is possible due to the similarity between O–H and S–Li bonds. The X-ray photoelectron spectroscopy (XPS) of Si 2p spectrum showed that two components appear: one at 102.1 eV related to Si–C which is the result of the reaction between CTMS and PEG, another at 103.2 eV related to Si–S which can prove the reaction between CTMS and LGPS (Fig. 1b– e). On the one hand, these chemical bonds can act as a bridge to increase Li-ion transport, so as to prevent the local potential difference and electrolyte oxidation caused by the ion aggregation between LGPS and PEG. On the other hand, the encapsulation of PEG and PEO can effectively improve the environmental stability of LGPS, so as to ensure the electrochemical and chemical stability of the composite electrolyte. The authors also tested the ionic conductivities of HSE membranes at different temperatures (from 0 to 50 C) (Fig. 1f). The results showed that PEO/ PEG membrane exhibited higher ionic conductivity (1.54 9 10 S cm at room temperature) and lower activation energy (0.37 eV) than PEO. After adding LGPS, the ionic conductivity was further improved. Among them, the room temperature conductivity of PEO/PEG-3LGPS is the highest (9.83 9 10 S cm). Finally, the authors measured the performance of different solid electrolytes in batteries and found that the battery with PEO/PEG-3LGPS membrane is the best among them which has a capacity retention of 94% after 120 cycles (Fig. 1g). In summary, the report by Zhang and coworkers demonstrates a promising candidate for hybrid solid electrolytes. In this work, flexible ceramic/polymer HSE films with different LGPS contents were prepared by in situ coupling reaction with CTMS and had excellent ionic C.-L. Yan* College of Energy, Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province, Soochow University, Suzhou 215006, China e-mail: [email protected]